Mature landfill leachate utilization using a cost-effective hybrid method

Highlights: • Co-digestion of sewage sludge and cavitated mature landfill leachate is studied. • The use of a small CL dose and optimal co-digestion HRT of 20 days is suggested. • Biogas production rate increases when optimal HRT is ensured. • FT-IR/PAS analysis seems to indicate that no new toxic compounds are formed. • The method is recommended as cost-effective for utilizing mature leachate. - Abstract: The main goal of this study was to investigate the co-digestion of sewage sludge and mature landfill leachate pretreated through hydrodynamic cavitation. The process efficiency was analyzed from the aspects of organics removal, biogas production, kinetics and digestate quality. Energy efficiency of the overall treatment was evaluated as well. A dose of hydrodynamically cavitated leachate of 5% v/v was used as a substrate for co-digestion with sewage sludge at a hydraulic retention time of 20 days. This improved the kinetics, biogas production and corresponding yields, as well as digestate quality. Fourier transform infrared photoacoustic spectroscopy analysis seemed to indicate that no new toxic compounds were formed with co-digestion. The investigated two-stage treatment is recommended as a safe and cost-effective method of utilizing mature leachate.